Metal-free carbocatalyst for room temperature acceptorless dehydrogenation of N-heterocycles

The XPS of pyridine: A combined theoretical and experimental analysis

A detailed analysis of the N(1s) and C(1s) X-Ray Photoelectron Spectroscopy (XPS) is made, where the measured XPS is compared with theoretical Sudden Approximation (SA) intensities and theoretical XPS Binding Energies (BEs). There is remarkably good agreement between the theoretical predictions and the measured XPS; in particular, the different full width at half maximum values for the C(1s) and N(1s) BEs are explained in terms of unresolved C(1s) BEs for the different C atoms in pyridine. This work demonstrates that the combination of theory and XPS measurements can extract analysis of the XPS relevant to the molecular electronic structure. The theory used is based on fully relativistic self-consistent field solutions of the Dirac-Coulomb Hamiltonian, and the SA is used to determine relative XPS intensities.

CO-Tolerant Heterogeneous Ruthenium Catalysts for Efficient Formic Acid Dehydrogenation

The development of improved and less costly catalysts for dehydrogenation of formic acid (HCOOH) is of general interest for renewable energy technologies involving hydrogen storage and release. Theoretical calculations reveal that ruthenium (Ru) nanoparticles supported on nitrogen-doped carbon should be appropriate catalysts for such transformations. It is predicted that nitrogen doping significantly decreases the formation of CO, but at the same time increases CO tolerance of the catalysts. To prove these hypotheses heterogeneous ruthenium catalysts supported on porous nitrogen-doped carbon (Rux/CN) with hierarchical structure were synthesized using carbon nitride (C3N4) as template and phenanthroline (Phen) as ligand. Experimental tests in HCOOH dehydrogenation revealed that the optimal catalyst Ru7/CN exhibited good thermal stability at 140 °C and a high turnover frequency (TOF >1300 h-1), which is more than one order of magnitude higher than that of the commercial Ru5/C catalyst.

Enable biomass-derived alcohols mediated alkylation and transfer hydrogenation

A single-atom catalyst with generally regarded inert Zn-N4 motifs derived from ZIF-8 is unexpectedly efficient for the activation of alcohols, enabling alcohol-mediated alkylation and transfer hydrogenation. C-alkylation of nitriles, ketones, alcohols, N-heterocycles, amides, keto acids, and esters, and N-alkylation of amines and amides all go smoothly with the developed method. Taking the α-alkylation of nitriles with alcohols as an example, the α-alkylation starts from the (1) nitrogen-doped carbon support catalyzed dehydrogenation of alcohols into aldehydes, which further condensed with nitriles to give vinyl nitriles, followed by (2) transfer hydrogenation of C=C bonds in vinyl nitriles on Zn-N4 sites. The experimental results and DFT calculations reveal that the Lewis acidic Zn-N4 sites promote step (2) by activating the alcohols. This is the first example of highly efficient single-atom catalysts for various organic transformations with biomass-derived alcohols as the alkylating reagents and hydrogen donors.

Revisiting the phosphonium salt chemistry for P-doped carbon synthesis: toward high phosphorus contents and beyond the phosphate environment

The introduction of phosphorus and nitrogen atoms in carbo-catalysts is a common way to tune the electronic density, and thereby the reactivity, of the material, as well as to introduce surface reactive sites. Numerous environments are reported for the N atoms, but the P-doping chemistry is less explored and focuses on surface POx groups. A one-step synthesis of P/N-doped carbonaceous materials is presented here, using affordable and industrially available urea and tetrakis(hydroxymethyl)phosphonium chloride (THPC) as the N and P sources, respectively. In contrast to most of the synthetic pathways toward P-doped carbonaceous materials, the THPC precursor only displays P-C bonds along the carbon backbone. This resulted in unusual phosphorus environments for the materials obtained from direct thermal treatment of THPC-urea, presumably of type C-P-N according to 31P NMR and XPS. Alternatively, the in situ polymerization and calcination of the precursors were run in calcium chloride hydrate, used as a combined reaction medium and porogen agent. Following this salt-templating strategy led to particularly high phosphorus contents (up to 18 wt%), associated with porosities up to 600 m2 g-1. The so-formed P/N-doped porous materials were employed as metal-free catalysts for the mild oxidative dehydrogenation of N-heterocycles to N-heteroarenes at room temperature and in air.

On the mechanism of acceptorless dehydrogenation of N-heterocycles catalyzed by tBuOK: a computational study

The catalytic acceptorless dehydrogenation (ADH) of saturated N-heterocycles has recently gained considerable attention as a promising strategy for hydrogen release from liquid organic hydrogen carriers (LOHCs). Recently, a simple tBuOK base-promoted ADH of N-heterocycles was developed by Yu et al. (Adv. Synth. Catal. 2019, 361, 3958). However, it is still open as to how the tBuOK plays a catalytic role in the ADH process. Herein, our density functional study reveals that the tBuOK catalyzes the ADH of 1,2,3,4-tetrahydroquinoline (THQ) through a quasi-metal-ligand bifunctional catalytic channel or a base-catalyzed pathway with close energy barriers. The hydride transfer in the first dehydrogenation process is determined to be the rate determining step, and the second dehydrogenation can proceed directly from 34DHQ regulated by the tBuOK. In addition, the computational results show that the cooperation of a suitable alkali metal ion with the tBuO- group is so critical that the tBuOLi and the isolated tBuO- are both inferior to tBuOK as a dehydrogenation catalyst.

Continuous Room-Temperature Hydrogen Release from Liquid Organic Carriers in a Photocatalytic Packed-Bed Flow Reactor

Despite the potential of hydrogen (H₂ ) storage in liquid organic carriers to achieve carbon neutrality, the energy required for H₂ release and the cost of catalyst recycling have hindered its large-scale adoption. In response, a photo flow reactor packed with rhodium (Rh)/titania (TiO₂ ) photocatalyst was reported for the continuous and selective acceptorless dehydrogenation of 1,2,3,4-tetrahydroquinoline to H₂ gas and quinoline under visible light irradiation at room temperature. The tradeoff between the reactor pressure drop and its photocatalytic surface area was resolved by selective in-situ photodeposition of Rh in the photo flow reactor post-packing on the outer surface of the TiO₂ microparticles available to photon flux, thereby reducing the optimal Rh loading by 10 times compared to a batch reactor, while facilitating catalyst reuse and regeneration. An example of using quinoline as a hydrogen acceptor to lower the energy of the hydrogen production step was demonstrated via the water-gas shift reaction.

Cobalt nanoparticles supported on microporous nitrogen-doped carbon for efficient catalytic transfer hydrogenation reaction between nitroarenes and N-heterocycles

Catalytic transfer hydrogenation reaction between nitroarenes and saturated N-heterocycles to simultaneously synthesize value-added anilines and unsaturated N-heterocycles is attractive due to its low-cost, atomic economic, and environmental-friendly properties. Herein, we...